The invention relates to a device for adjusting the relative ratio of the colors red, green and blue in the light when making a print of a color film according to the additive method by means of a photographic enlarger and more particularly to such a device which comprises additive color filters which are transparent to red, green, and blue light, respectively, and which are situated during printing in a convergent light beam originating from the light source. Such a device is known from U.S. Pat. No. 3,923,394.
As used herein, a color film is a picture of a scene recorded on a film, and may be either a negative or a positive (a color slide) image as well. During printing, the color film is arranged at an area in the enlarger, for example, between the objective and an illumination system present in the enlarger.
The aforementioned U.S. Patent discloses an enlarging device comprising three light sources. Each light source is included in a respective elliptical reflector, and a color filter is arranged at the light-emanating side of each reflector. According to that Patent, such filters can be constructed as additive primary filters (red, green and blue). When printing according to the additive method, the spectral composition of the light incident upon the color film can be varied arbitrarily, for example by means of the supply current from the light sources, which are, for example, in the form of halogen incandescent lamps. According to the principle described, prints of high quality can be obtained.
A disadvantage of this additive enlarger is that the housing of the device in which the three light sources with the associated reflectors are present is voluminous. Moreover, the housing accommodates a mixing chamber which is also necessarily comparatively voluminous due to the use of three light sources. By means of such a mixing chamber, the light transmitted by the filters is mixed so that the light incident upon the color film is of homogeneous color. The use of three light sources further has the disadvantage that each light source has coupled to it a separate control unit for controlling the operating time and/or the light intensity.